314 INFLUENCE OF THE NERVOUS SYSTEM 



separated from the rest, We can at present only speculate ; but it may not be 

 considered improbable that, by their peculiar plexiform arrangement in the 

 various ganglia through which they pass, connections are established between 

 remote organs, which tend to bring their actions into closer relation with each 

 other than would otherwise be the case. The existence of such connections, 

 for the purpose of harmonizing the several movements of the Viscera which 

 are concerned in the various and complex operations of Digestion and its 

 attendant processes, may be inferred from the perfect conformity which exists 

 between them, during all their different states of regular action ; and still 

 more, perhaps, from the phenomena of their disordered conditions. The 

 study of these Sympathies is one of those departments of Physiology, in which 

 it may be expected that much will be gained, by patient and well-directed 

 investigation. 



423. The movements immediately concerned in the Organic Functions, 

 however, are not influenced by Reflex action alone, but also by Emotional 

 conditions of the mind. This is most obvious in regard to the Heart. Every 

 one must have experienced the disturbance of its pulsations, consequent upon 

 excitement of the feelings, of almost any description. But other organs pro- 

 bably experience similar changes, although of a less manifest character. It is 

 well known that the Sympathetic system is largely distributed upon the trunks 

 of the blood-vessels, accompanying them to their minutest ramifications ; and 

 it will be hereafter shown ( 504), that the fibrous tissue of the walls of the 

 arteries is probably susceptible 01 influence from these nerves. There can be 

 little doubt, therefore, that they constitute the channel through which Emotions 

 operate, in producing, sudden distension of particular parts of the vascular 

 system, as in blushing, erection, &c. And to the same kind of influence, 

 more gradually exerted, we may very probably attribute the regulation of the 

 supply of blood which passes to different secreting organs, in varying condi- 

 tions of the system. 



424. But the Sympathetic System does not consist of Cerebro-Spinal fila- 

 ments alone ; nor is its influence exerted only upon the motor or contractile 

 tissues of the body. There is good evidence, that the Nervous System has 

 an immediate action upon the molecular changes which constitute the func- 

 tions of Nutrition, Secretion, &c. ; and the channel of that 'influence is pro- 

 bably to be found in that system of organic fibres formerly described ( 1 10), 

 which constitutes a considerable portion of the Visceral nerves, existing much 

 more sparingly in most of the Cerebro-Spinal, but being abundant in the Fifth 

 pair. There is no valid reason, however, to believe that any of the processes 

 of Nutrition and Secretion are dependent upon this, or any other kind of 

 Nervous agency. These processes go on with great rapidity and energy in 

 the Vegetable kingdom, in which nothing approaching to a Nervous System 

 exists ; and in the Animal kingdom they take place with equal vigour, long 

 before the least vestige of it appears. The Embryological researches of Dr. 

 Barry have fully proved that in the earliest condition of foetal life, the germ 

 consists but of a congeries of cells, which have all originated in a single one ; 

 and from this mass the several tissues are gradually generated, by a process 

 which is technically called histological* transformation, one set of cells being 

 converted into muscular tissue, another into nervous tissue, another into 

 mucous membrane, and so on. Now since this is the case, it is evident that 

 all these processes of development must take place, in virtue of the inherent 

 properties of the primary tissue itself; since no nervous influence can be 

 supposed to operate before nerves are called into existence. Throughout the 



* This term is used in contradistinction to morphological, which applies to the altera- 

 tions in the/yr/7 of the several parts of the embryo. 



